Inductive structures with improved common mode transient immunity

ABSTRACT

In a first inductive structure, a first data coil includes: a first portion for conducting a first common mode current in a first direction; and a second portion for conducting a second common mode current in a second direction opposite the first direction. The first and second portions of the first data coil are connected at a first node. In a second inductive structure, a second data coil includes: a first portion for conducting a third common mode current in the first direction; and a second portion for conducting a fourth common mode current in the second direction. The first and second portions of the second data coil are connected at a second node galvanically isolated from the first node. The first, second, third and fourth common mode currents are induced by a common mode transient.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to: (a) U.S. Provisional Patent Application Ser. No. 61/841,765, filed Jul. 1, 2013, entitled A METHOD TO IMPROVE COMMON MODE TRANSIENT IMMUNITY FOR INDUCTIVE STRUCTURES, naming Rajaram Subramonian et al. as inventors; and (b) U.S. Provisional Patent Application Ser. No. 61/876,796, filed Sep. 12, 2013, entitled A METHOD TO IMPROVE COMMON MODE TRANSIENT IMMUNITY FOR INDUCTIVE STRUCTURES, naming Rajaram Subramonian et al. as inventors. All of the above-identified applications are hereby fully incorporated herein by reference for all purposes.

This application is related to co-owned co-pending U.S. patent application Ser. No. 14/026,515, filed on Sep. 13, 2013, entitled INDUCTIVE STRUCTURES WITH REDUCED EMISSIONS AND INTERFERENCE, naming Gianpaolo Lisi et al. as inventors.

BACKGROUND

The disclosures herein relate in general to electronic circuitry, and in particular to inductive structures with improved common mode transient immunity.

An inductively coupled structure (or “inductive structure”) is useful for transmitting data (or both data and power) from one or more transmitters to one or more receivers across an isolation barrier that exists between two systems (and/or sub-systems) that have galvanically isolated (e.g., having the effect of blocking direct-current electricity) ground planes. Interference may arise in communicating data between systems when an electronic transient event occurs with respect to (e.g., across) the ground planes of two galvanically isolated systems. If such data are transmitted through a single channel of an inductive structure, then various challenges and limitations may arise. However, if such data are transmitted through multiple channels of an inductive structure, then other challenges and limitations may arise (e.g., increased size, cost, emissions and/or interference).

SUMMARY

In a first inductive structure, a first data coil includes: a first portion for conducting a first common mode current in a first direction; and a second portion for conducting a second common mode current in a second direction opposite the first direction. The first and second portions of the first data coil are connected at a first node. In a second inductive structure, a second data coil includes: a first portion for conducting a third common mode current in the first direction; and a second portion for conducting a fourth common mode current in the second direction. The first and second portions of the second data coil are connected at a second node galvanically isolated from the first node. The first, second, third and fourth common mode currents are induced by a common mode transient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a system of the illustrative embodiments.

FIG. 2 is a schematic plan view of an inductive structure of FIG. 1.

FIG. 3 is a schematic perspective view of the inductive structure of FIG. 1.

FIG. 4 is a structural perspective view of the inductive structure of FIG. 1.

FIG. 5a is an enlarged view of a first portion of FIG. 4.

FIG. 5b is an enlarged view of a second portion of FIG. 4.

FIG. 6 is a schematic diagram of a simulation model of the inductive structure of FIG. 1.

FIG. 7 is an example waveform diagram of the inductive structure of FIG. 1.

FIG. 8 is a histogram of spectral densities illustrating common mode transient immunity of the inductive structure of FIG. 1.

FIG. 9 is a layout view of an alternative version of the inductive structure of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a system, indicated generally at 100, of the illustrative embodiments. A transmitter 102 outputs data and power to a receiver 104 through a device that includes inductive structures 106 a and 106 b (collectively, “inductive structure 106”). The inductive structure 106 a: (a) receives the data from the transmitter 102 through differential TX Data lines; (b) receives the power from the transmitter 102 through differential TX Power lines; and (c) outputs the data and power by inductive coupling across an isolation barrier 108 to the inductive structure 106 b. The inductive structure 106 b: (a) receives the data and power by inductive coupling across the isolation barrier 108 from the inductive structure 106 a; (b) outputs the data to the receiver 104 (which receives the data) through differential RX Data lines; and (c) outputs the power to the receiver 104 (which receives the power) through differential RX Power lines. As discussed below, optimized impedance devices Z1 and Z2 are optionally included in inductive structure 106 b and 106 b, respectively.

Transmitter 102 optionally includes: (a) a modulator 110 and (b) a driver 112. The modulator 110 uses the data to be transmitted to modulate a carrier signal (e.g., 1 GHz) and outputs the modulated carrier signal. The driver 112 includes drivers for increasing the electrical drive strength of the output of the modulator 110. The driver 112 includes capacitors for blocking direct current (“DC”) of the output of the driver 112. The outputs of the driver 112 are coupled to data inputs of the inductive structure 106.

The inductive structure 106 is a resonant filter for substantially filtering out frequencies outside of a passband (e.g., while blocking transference of direct current from the inductive structure 106 a to the inductive structure 106 b). The passband is substantially centered around the carrier signal frequency (e.g., 1 GHz) and accordingly permits inductive coupling of data across the isolation barrier 108 from the inductive structure 106 a to the inductive structure 10 b.

The receiver 104 optionally includes: (a) a high pass filter and common mode voltage generator block 114 and (b) a demodulator 116. The generator block 114: (a) receives a bias voltage; (b) high-pass filters the differential RX Data lines; and (c) generates a common mode voltage in response to the differential RX Data lines. The demodulator 116 demodulates the high-pass filtered differential RX Data lines to recover the data carried by the high-pass filtered differential RX Data lines.

FIG. 2 is a schematic plan view of the inductive structure 106 for transfer of data and optionally for transfer of power. As shown in FIG. 2, the inductive structure 106 a includes: (a) an optional power coil 202 connected to the differential TX Power lines, namely TX Power+ and TX Power−; and (b) data coils 204 a and 204 b (collectively, “data coil 204”) connected to the differential TX Data lines, namely TX Data+ (connected to the data coil 204 a) and TX Data− (connected to the data coil 204 b). Also, the data coil 204 a is connected to the data coil 204 b at a node 206, which is coupled through a center tap ground line 208 to a first ground or to an optimized (e.g., for transmission line matching) impedance device Z1.

The data coil 204 is substantially centered within the power coil 202. Accordingly, the data coil 204 is smaller than the power coil 202. Because the data coil 204 is located (e.g., formed) within the center of the power coil 202, the inductive structure 106 has reduced size and cost.

Also, the data coil 204 is formed to have a relatively symmetric shape (e.g., symmetric 8-shape). As shown in FIG. 2, the data coil 204 b is substantially identical to (yet reversed from) the data coil 204 a. If current flows through the data coil 204 a in one direction (e.g., clockwise), then current flows through the data coil 204 b in an opposite direction (e.g., counterclockwise). Alternatively, in the case of data transmission only (e.g., without operating power coil 202), the data coils 204 a and 204 b are reconfigurable to flow current in the same direction as one another. The center tap ground line 208 helps to substantially equalize a voltage between TX Data+ and the center tap ground line 208 (“TX Data+ voltage”), relative to a voltage between TX Data− and the center tap ground line 208 (“TX Data+ voltage”).

In this example, an alternating current flows through the power coil 202. A magnetic field induced by the power coil 202 on the data coil 204 a results in an electromotive force that is substantially equal in magnitude to (yet opposite in polarity from) an electromotive force induced by the power coil 202 on the data coil 204 b, so an effect of magnetic flux from the power coil 202 on the data coil 204 a is substantially counterbalanced (e.g., cancelled) by an effect of magnetic flux from the power coil 202 on the data coil 204 b. Accordingly, the power coil 202 induces a relatively small difference (if any) between TX Data+ voltage and TX Data− voltage, even if the data coils 204 a and 204 b might have slight differences (e.g., in size and/or shape) from one another.

FIG. 3 is a schematic perspective view of the inductive structure 106. FIG. 4 is a structural perspective view of the inductive structure 106. FIGS. 3 and 4 are not necessarily drawn to scale. As shown in FIGS. 3 and 4, the inductive structure 106 b is substantially identical to the inductive structure 106 a. Further, as illustrated at 400, the power coils 202 and 302 have multiple turns, and the data coils 204 and 304 have multiple turns.

Accordingly, the inductive structure 106 b includes: (a) an optional power coil 302 connected to the differential RX Power lines, namely RX Power+ and RX Power−; and (b) data coils 304 a and 304 b (collectively, “data coil 304”) connected to the differential RX Data lines, namely RX Data+ (connected to the data coil 304 a) and RX Data− (connected to the data coil 304 b). Also, the data coil 304 a is connected to the data coil 304 b at a node 306, which is connected to a center tap ground line 308 to a second ground or to an optimized impedance device Z2 that is isolated from: (a) the first ground (e.g., isolated from the center tap ground line 208); and/or (b) optimized impedance device Z1.

Also, the data coil 304 is formed to have a relatively symmetric shape (e.g., symmetric 8-shape). As shown in FIGS. 3 and 4, the data coil 304 b is substantially identical to (yet reversed from) the data coil 304 a. If current flows through the data coil 304 a in one direction (e.g., clockwise), then current flows through the data coil 304 b in an opposite direction (e.g., counterclockwise). Alternatively, in the case of data transmission only (e.g., without operating power coil 302), the data coils 304 a and 304 b are reconfigurable to flow current in the same direction as one another. The center tap ground line 308 helps to substantially equalize a voltage between RX Data+ and the center tap ground line 308 (“RX Data+ voltage”), relative to a voltage between RX Data− and the center tap ground line 308 (“RX Data+ voltage”).

Further, as shown in FIGS. 3 and 4, the inductive structures 106 a and 106 b are aligned with one another (e.g., the data coils 204 a and 304 a are aligned with one another, and the data coils 204 b and 304 b are aligned with one another), so that: (a) the power coils 202 and 302 have relatively good coupling with one another; (b) the data coils 204 and 304 have relatively good coupling with one another; and (c) radiated emissions are relatively small (e.g., as radiated by the data coils 204 and 304), which helps with electromagnetic interference (“EMI”) certification.

FIG. 5a is an enlarged view of a first portion of FIG. 4. FIG. 5a is not necessarily drawn to scale. As shown in FIGS. 4 and 5 a, the data coil 204 is substantially centered within the power coil 202. Accordingly, the turns (e.g., traces) of the data coil 204 a that are surrounded by one or more respective turns of the power coil 202 contribute to a capacitance (e.g., parasitic capacitance), which is distributed between the data coil 204 a and the power coil 202, such as a capacitance within a region 402 of FIG. 5a . Such capacitance adversely affects electrical characteristics of the inductive structures 106 a and/or 106 b. In one example, such capacitance is distributed throughout any dielectric that separates the data coil 204 a from the power coil 202. Similar capacitance exists between: (a) the power coil 202 and the data coil 204 b; (b) the power coil 202 and the power coil 302; (c) the power coil 302 and the data coil 204 a; (d) the power coil 302 and the data coil 204 b; (e) the power coil 302 and the data coil 304 a; (f) the power coil 302 and the data coil 304 b; (g) the power coil 202 and the data coil 304 a; (h) the power coil 202 and the data coil 304 b; (i) the data coil 204 a and the data coil 304 a; and (j) the data coil 204 b and the data coil 304 b.

FIG. 5b is an enlarged view of a second portion of FIG. 4. FIG. 5b is not necessarily drawn to scale. As shown in FIGS. 4 and 5 b, the power coil 202 is arranged in a plane that is above a plane in which the differential RX Data lines and the center tap ground line 308 are arranged. A capacitance is distributed between the center tap ground line 308 and the various turns of the power coil 202, such as a capacitance within a region 404 of FIG. 5b . In one example, such capacitance is distributed throughout any dielectric that separates the center tap ground line 308 from the power coil 202.

Also, proximity of the RX Data+ and RX Data− lines to one another contributes to a distributed capacitance that adversely affects electrical characteristics of the inductive structures 106 a and/or 106 b, such as a distributed capacitance within a region 406 between the RX Data+ and RX Data− lines. In one example, such capacitance is distributed throughout any dielectric that separates the RX Data+ and RX Data− lines. Similar capacitance exists between: (a) the RX Data+ and TX Data+ lines; (b) the RX Data+ and TX Data− lines; (c) the RX Data− and TX Data+lines; (d) the RX Data− and TX Data− lines; and (e) the TX Data+ and TX Data− lines.

The distributed capacitance adversely affects electrical characteristics of the inductive structure 106, such as by capacitively coupling common mode transient events (“common mode transients”) from a first data coil (e.g., data coil 204) to a second data coil (e.g., data coil 304), where the second data coil is galvanically isolated from the first data coil. In embodiments having a power coil 302, common mode transients are capacitively coupled from the surrounding power coil (e.g., power coil 302) and its overlying power coil (e.g., power coil 202) to the second data coil (e.g., data coil 304).

The electromotive coupling in inductive structure 106 (e.g., that results from mutual inductance, magnetic coupling, and distributed capacitances across a dielectric of the isolation barrier 108) is reduced by the arrangement of substantially symmetrical data coils, where each data coil has first and second portions that generate mutually counterbalancing currents in operation. In one example, the mutually counterbalancing currents are generated by turns of the first portion formed in a clockwise direction and by turns of the second portion formed in a counterclockwise direction.

The effect of the distributed (e.g., parasitic) capacitance upon the data coil 304 (such as induced by effects of a common mode transient applied to data coil 204 and/or power coil 202) is substantially reduced (and perhaps even completely eliminated) by the data coil 304 center tap being coupled to the center tap ground line 308. When a common mode transient occurs, it induces a common mode current in a first direction of the first portion (e.g., 204 a) of the data coil 204 and a common mode current in a second direction of the second portion (e.g., 204 b) of the data coil 204. The distributed capacitance of the isolation barrier 108 is capacitively coupled to the data coil 304, so that the common mode current in the first direction induces a common mode current in the first direction of the first portion (e.g., 304 a) of the data coil 304 and the common mode current in the second direction induces a common mode current in the second direction of the second portion (e.g., 304 b) of the data coil 304. The common mode current in the first direction of the first portion of the data coil 304 is substantially equal in magnitude to (yet opposite in polarity from) the common mode current in the second direction of the second portion of the data coil 304, so that both of those currents are substantially counterbalanced (e.g., cancelled) at the data coil 304 center tap.

Similarly, the effect of any common mode transient in symmetrical structures, such as optional power coil 202 and optional power coil 302 that are capacitively coupled to the data coil 304, is substantially reduced. The effect of such common mode transient is reduced by symmetrical capacitive coupling to the first and second portions of the data coil 304 (which induces associated common mode currents of opposite polarity therein) and by counterbalancing of the induced associated common mode currents at the data coil 304 center tap.

The extent of symmetry of the components of inductive structures 106 a and 106 b affects an extent to which the first and second portions generate (e.g., induce) mutually counterbalancing currents. For example, manufacturing tolerances may permit a relatively small amount of asymmetrical variation to form in components of inductive structures 106 a and 106 b, due to inconsistencies in manufacturing processes. The resulting asymmetry may result in electrical parameter mismatches, such as mismatch between: (a) respective capacitances and/or resistances of inductive structures 106 a and 106 b; (b) respective capacitances and/or resistances of the first and second portions of each data coil (e.g., 204 and 304); (c) respective capacitances of data coil 204 (e.g., as measured between TX Data+ and TX Data− terminal ends) and data coil 304 (e.g., as measured between RX Data+ and RX Data− terminal ends); (d) respective capacitances of power coil 202 and data coil 304; and (e) respective capacitances of power coil 302 and data coil 204. Accordingly, the resulting asymmetry contributes to CMT coupling (e.g., as discussed below with respect to FIG. 7 and FIG. 8).

FIG. 6 is a schematic diagram of a simulation model 600 of the inductive structure 106. As shown in FIG. 6, the model 600 includes: (a) signal generators X1, X2 and X3; (b) resistors R1, R2, R3, R4, R5, R6, R7 and R8; (c) coils L1, L2, L3 and L4; and (d) capacitors C1, C2, C3, C4 and C5.

In operation, signal generators X2 and X3 provide stimulus for simulating the reception of TX Data+ and TX Data−, respectively. For example, the signal sources provide currents that generate a voltage across a network including resistors R1, R2 and R7 and coils L1 and L2 (which simulate an operation of data coil 204 a and data coil 204 b, respectively). Because of the relatively high impedances of resistors R1 and R2 (e.g., 100 kilohms each), a current 604 primarily flows: (a) in a first direction from TX Data+ through coils L1 and L2 to TX Data− when TX Data+ is high and (b) in a second direction from TX Data− through coils L2 and L1 to TX Data+ when TX Data+ is low.

The mutual inductance of coil L1 with coil L3, and the mutual inductance of coil L2 with coil L4, induce a current 608 to primarily flow: (a) in a first direction from RX Data− through coils L4 and L3 to RX Data+ when TX Data+ is high; and (b) in a second direction from RX Data+ through coils L3 and L4 to RX Data− when TX Data+ is low. Resistors R3 and R4 (e.g., 1 kilohm), resistor R5 (e.g., 10 kilohms), and capacitor C4 (100 femto-Farads) simulate the input impedance that helps develop the RX Data+ and RX Data− voltages.

Stimulus block 602 applies a common mode transient via the center tap of each coil of the primary coils (e.g., coils L1 and L2) and secondary coils (e.g., coils L3 and L4), so that a common mode transient is capacitively coupled across the isolation barrier 108. For example, a positive output of stimulus block 602 is coupled to a first terminal of resistor R7. In this example, resistor R7 is 5 ohms, which simulates resistance in the ground path of the center tap of the primary coils (e.g., coils L1 and L2) through node 206 (which is coupled to a second terminal of resistor R7). Also, a negative output of stimulus block 602 is coupled to a first terminal of resistor R8. In this example, resistor R8 is 5 ohms, which simulates resistance in the ground path of the center tap of the secondary coils (e.g., coils L3 and L4) through node 306 (which is coupled to a second terminal of resistor R8).

Accordingly, the respective center taps (e.g., nodes 206 and 306) of the primary and secondary coils are also the grounds or optimized impedances (e.g., impedance devices Z1 and Z2, respectively, to the grounds) of the circuitry on respective sides of the isolation barrier 108. The respective center taps of the primary and secondary coils provide low impedance paths (e.g., to ground) for common-mode transient-induced current, which helps to: (a) reduce the effect of common mode transients upon the differential RX Data lines; and (b) accordingly, ensure robust data transfer, and allow simpler transmitter 102 and receiver 104 designs.

Stimulus block 602 generates a common mode transient using signal generator X1. Signal generator X1 generates a pulse having a relatively high rate of change in a rising edge and falling edge of the pulse. The pulse simulates a relatively large (e.g., for robust testing) common mode transient voltage (e.g., measured in kilovolts per microsecond), which is applied across the primary and secondary coils as described below. Resistor R6 and capacitor C5 low-pass filter the output of the stimulus block 602 to compensate for discontinuities in slope caused by piecewise functionality of the signal generator X1. For example, the discontinuities in slope occur at the junction (e.g., “sharp corner”) of the rising edge and the peak level, and likewise occur at the junction of the peak level and falling edge of the common mode transient pulse.

When the stimulus block 602 applies (e.g., injects) a common mode transient between the two isolated grounds, the distributed capacitance (e.g., modeled by capacitors C1, C2 and C3) of the isolation barrier 108 capacitively transfers a current 606 across the isolation barrier 108. The transferred current 606 is proportional to the distributed capacitance of the isolation barrier 108 and is proportional to the rate of change of the applied transient voltage.

If coupling between the coils L1, L3 pair and L2, L4 pair is hypothetically 100% efficient, then coil inductances of L3 and L4 would not substantially affect the transferred current 606 (e.g., coupled via capacitors C1 and C3), because the flux of L1 would substantially cancel the flux of L3, and the flux of L2 would substantially cancel the flux of L4, and the very small coil resistances would have a very small effect on the transferred current 606. By comparison, if such coupling is less than 100% efficient (e.g., as in a real physical structure), then the transferred current 606 would encounter impedance from the leakage inductances and coil resistances of L3 and L4.

The effect of applied common mode transient upon the differential RX Data lines is substantially zero when the transient-induced current conducted coil L3 is substantially the same magnitude and opposite in polarity to the transient-induced current conducted by L4. In the event of any mismatch in symmetry between inductive structures 106 a and 106 b, the transient-induced current conducted by L3 would not completely cancel the transient-induced current conducted by L4, and the non-cancelled portion of transient induced current would have a small effect on the differential RX Data lines, as discussed below with reference to FIG. 7 and FIG. 8.

FIG. 7 is an example waveform diagram 700 of the inductive structure 106. The diagram 700 includes: (a) a horizontal axis 702 having units of nanoseconds; and (b) a vertical axis 704 having units of voltage (e.g., volts or millivolts).

Trace 710 is a waveform representing common mode transient pulses 712, 714 and 716. Common mode transient pulse 712 has a peak voltage of 400 volts, a rising edge that is initiated near the 40 nanosecond mark, and a falling edge that is initiated near the 60 nanosecond mark. Common mode transient pulse 714 has a peak voltage of 400 volts, a rising edge that is initiated near the 140 nanosecond mark, and a falling edge that is initiated near the 170 nanosecond mark. Common mode transient pulse 716 has a peak voltage of 400 volts, a rising edge that begins near the 250 nanosecond mark, and a falling edge that begins near the 280 nanosecond mark.

Trace 720 is a waveform representing alternating current of approximately 5 volts to approximately −5 volts flowing through the power coil 202. The alternating current flows through the power coil 202 for a period 722 that begins near the 100 nanosecond mark for a duration of ˜100 nanoseconds. Trace 724 is a waveform representing alternating current flowing through the power coil 302. The waveform of trace 724 is inductively coupled from the alternating current flowing through the power coil 202 and accordingly is phase-delayed relative to trace 720.

Trace 730 is a waveform representing data to be transmitted (before modulation) at a data rate of ˜50 MHz. Trace 730 includes a series of data encoded using waveforms that alternate between ˜2 volts and ground. The series of data includes 10 nanosecond-long pulses and begins near the 130 nanosecond mark.

Trace 740 is a waveform representing data being transmitted (after modulation) across the TX Data+ line. Trace 740 represents a series of modulated bits, which are modulated by a 2 GHz carrier signal that alternates between approximately 800 millivolts and −800 millivolts. For example, the presence of a carrier signal indicates a logic 1 state of data being transmitted.

Trace 750 is a waveform representing data being received (after modulation) across the RX Data+ line. Trace 750 represents a series of modulated bits, where the presence of a carrier signal that alternates between approximately 500 millivolts and −500 millivolts indicates a logic 1 state of data being received. Trace 750 also indicates the cross-coupling of the power coil related signals of traces 720 and 724 to the RX Data+ line. For example, the coupling causes power coil interference 752 on the RX Data+ line when no data is being received via the RX Data+ line. Also, the coupling causes power coil interference 754 on the RX Data+ line when data is being received via the RX Data+ line. In contrast, the common mode transient signal coupling to the TX Data+ line is negligible and is virtually imperceptible at the scale of trace 750.

Trace 760 is a waveform representing the RX Data+ line after high-pass filtering by generator block 114. As illustrated by trace 760, the high-pass filtering removes the power coil interferences 752 and 754 to generate a well-formed modulated data signal, whose data is robustly and readily detectible by demodulator 116.

FIG. 8 is a histogram 800 of spectral densities illustrating common mode transient immunity of the inductive structure 106. Histogram 800 includes: (a) a horizontal axis 802 having units of gigahertz (GHz); and (b) a vertical axis 804 having units of power represented as decibels (dB). Spectral display 810 illustrates the power density of a common mode transient (such as common mode transient pulse 712) as applied to node 206, where the power (as a function of frequency) drops from approximately 50 dB near direct current to approximately −25 dB near 500 MHz. Spectral display 820 illustrates the power density of a common mode transient (such as common mode transient pulse 712) as measured at node 306, where the power averages approximately −75 dB in a frequency range of approximately 0-500 MHz. Accordingly, the center tap architecture of data coils 204 and 304 provides common mode transient immunity of greater than ˜50 dB.

FIG. 9 is a layout view of an alternative version of the inductive structure 106. As shown in FIG. 9, the alternative version has a structure 900, which is formed on a substrate 902 (e.g., printed circuit board) and includes: (a) a transmitter (TX) 910 (which is similar to transmitter 102); and (b) a receiver (RX) 920 (which is similar to receiver 104). The structure 900 further includes: (a) inductive structures 912 a and 912 b (collectively, “inductive structure 912”); and (b) inductive structures 922 a and 922 b (collectively, “inductive structure 922”). The inductive structures 912 and 922 are each similar to the inductive structure 106, but they do not have the “coiled” shape of data coils 204 and 304 (and do not include power coils 202 and 302). The inductive structures 912 and 922 are substantially identical to one another and/or are mirror images of one another around an axis of symmetry. In accordance with the description of FIG. 1, data is inductively transmitted from inductive structure 912 to inductive structure 922 across an isolation boundary.

Inductive structure 912 a is connected to the inductive structure 912 b at a node to which the center tap ground line 914 is coupled. The center tap ground line 914 is connected to a first ground or to a first optimized impedance device (e.g., impedance device Z1). Similarly, inductive structure 922 a is connected to the inductive structure 922 b at a node to which the center tap ground line 924 is coupled. The center tap ground line 924 is connected to a second ground or to a second optimized impedance device (e.g., impedance device Z2) that is isolated from the first ground and/or from the first optimized impedance device.

Although illustrative embodiments have been shown and described by way of example, a wide range of alternative embodiments is possible within the scope of the foregoing disclosure. 

What is claimed is:
 1. A device, comprising: a first inductive structure including a first data coil, wherein: a first portion of the first data coil is for conducting a first common mode current in a first direction; a second portion of the first data coil is for conducting a second common mode current in a second direction opposite the first direction; the first portion of the first data coil is connected at a first node to the second portion of the first data coil; and the first node is coupled to a first ground; and a second inductive structure including a second data coil, wherein: a first portion of the second data coil is aligned with the first portion of the first data coil for conducting a third common mode current in the first direction; a second portion of the second data coil is aligned with the second portion of the first data coil for conducting a fourth common mode current in the second direction; the first portion of the second data coil is connected at a second node to the second portion of the second data coil; the second node is coupled to a second ground galvanically isolated from the first ground; and the first, second, third and fourth common mode currents are induced by a common mode transient that occurs with respect to the first and second grounds; wherein the first and second portions of the first data coil are coupled to: receive data from a transmitter; and output the data by inductive coupling to the second data coil; and wherein the first and second portions of the second data coil are coupled to: receive data by inductive coupling from the first data coil; and output the data to a receiver.
 2. The device of claim 1, and comprising: an isolation barrier between the first and second inductive structures, wherein: the common mode current conducted in the first direction in the second data coil is capacitively induced across the isolation barrier by the common mode current conducted in the first direction in the first data coil; and the common mode current conducted in the second direction in the second data coil is capacitively induced across the isolation barrier by the common mode current conducted in the second direction in the first data coil.
 3. The device of claim 1, wherein the first inductive structure includes a first power coil, the first data coil is substantially centered within the first power coil, and the first power coil is for: receiving power from a transmitter; and outputting the power by inductive coupling to the second power coil.
 4. The device of claim 3, wherein the second inductive structure includes a second power coil, the second data coil is substantially centered within the second power coil, and the second power coil is for: receiving power by inductive coupling from the first power coil; and outputting the power to a receiver.
 5. The device of claim 4, wherein the first and second inductive structures are substantially identical to one another.
 6. The device of claim 5, wherein the first data coil is substantially centered within the first power coil.
 7. The device of claim 6, wherein the first and second portions of the first data coil are substantially identical to one another, yet reversed from one another.
 8. A method, comprising: conducting a first common mode current in a first direction through a first portion of a first data coil of a first inductive structure; conducting a second common mode current in a second direction through a second portion of the first data coil, wherein: the second direction is opposite the first direction; the first portion of the first data coil is connected at a first node to the second portion of the first data coil; and the first node is coupled to a first ground; conducting a third common mode current in the first direction through a first portion of a second data coil of a second inductive structure, wherein: the third common mode current is capacitively induced in response to the first current; and the first portion of the second data coil is aligned with the first portion of the first data coil; conducting a fourth common mode current in the second direction through a second portion of the second data coil, wherein: the fourth common mode current is capacitively induced in response to the second current; the second portion of the second data coil is aligned with the second portion of the first data coil; the first portion of the second data coil is connected at a second node to the second portion of the second data coil; and the second node is coupled to a second ground isolated from the first ground; with the first and second portions of the first data coil, receiving data from a transmitter, and outputting the data by inductive coupling to the second data coil; and with the first and second portions of the second data coil, receiving data by inductive coupling from the first data coil, and outputting the data to a receiver.
 9. The method of claim 8, and comprising: applying a common mode transient to the first inductive structure and capacitively coupling the common mode transient to the second inductive structure across an isolation barrier between the first and second inductive structure, wherein the third common mode current is substantially equal in magnitude to and opposite in polarity from the fourth common mode current.
 10. The method of claim 8, and comprising: inducing a fifth common mode current in the first direction through the first portion of a second data coil; and inducing a sixth common mode current in the second direction through the second portion of the second data coil; wherein: the fifth and sixth common mode currents are induced by capacitively coupling a first power coil to the data coil of the second inductive structure; and the first inductive structure includes the first power coil within which the first data coil is substantially centered.
 11. The method of claim 8, and comprising: inducing a seventh common mode current in the first direction through the first portion of a second data coil; and inducing an eighth common mode current in the second direction through the second portion of the second data coil; wherein: the seventh and eighth common mode currents are induced by capacitively coupling a second power coil to the data coil of the second inductive structure; and the second inductive structure includes the second power coil within which the second data coil is substantially centered.
 12. The method of claim 8, wherein the third and fourth common mode currents are substantially the same magnitude and are opposite in polarity to one another.
 13. The method of claim 12, and comprising: high-pass filtering a signal that includes the data received by the second data coil.
 14. A device, comprising: a first inductive structure including a first data coil; a second inductive structure including a second data coil, wherein the second data coil has a shape that is symmetric with respect to a shape of the first data coil, and wherein the first and second data coils are aligned with each other; an isolation barrier between the first and second inductive structures, wherein the first data coil is for: receiving data from a transmitter; and outputting the data by inductive coupling across the isolation barrier to the second data coil; and wherein the second data coil is for: receiving the data by inductive coupling across the isolation barrier from the first data coil; outputting the data to a receiver; receiving a capacitively coupled transient from the first inductive structure; generating a current of a first polarity in response to the capacitively coupled transient; and generating a current of a second polarity that is opposite the first polarity in response to the capacitively coupled transient; wherein the magnitude of the current of the first polarity is substantially the same as the magnitude of the current of the second polarity.
 15. The device of claim 14, wherein the first and second inductive structures are at least one of: substantially identical to one another; and mirror images of one other.
 16. The device of claim 15, wherein a center of the shape of the first data coil is coupled to a first ground via a first impedance device, a center of the shape of the second data coil is coupled to a second ground via a second impedance device, and the second ground is galvanically isolated from the first ground. 